Dissertations and Theses - Physics
http://hdl.handle.net/2142/8859
Dissertations in PhysicsTue, 22 Aug 2017 18:41:44 GMT2017-08-22T18:41:44ZAngular distributions of high-mass dilepton production in hadron collisions
http://hdl.handle.net/2142/93035
Angular distributions of high-mass dilepton production in hadron collisions
McClellan, Randall Evan
The SeaQuest experiment is a fixed-target dimuon experiment currently running at the Fermi National Accelerator Laboratory (FNAL). By utilizing the high-intensity, 120GeV proton beam delivered by the FNAL Main Injector (MI), SeaQuest is able to measure proton-induced Drell-Yan dimuon production off of various nuclear targets in kinematic regions inaccessible to previous similar experiments. A suitably large fraction of the final dataset has been recorded, reconstructed, and analyzed. Very preliminary results from light-sea flavor asymmetry, nuclear dependence, and partonic energy loss analyses have been presented at numerous international conferences.
A novel, FPGA-based trigger system has been designed, implemented, and optimized for the SeaQuest experiment. By implementing the trigger decision logic in FPGA firmware, it is more adaptable to changing experimental conditions. Additionally, the peripheral tasks of timing alignment, "trigger matrix" generation, and firmware uploading have been mostly automated, reducing the likelihood of user error in the maintenance and operation of the trigger system. Significant upgrades to hardware and firmware have greatly improved the performance of the trigger system since the 2012 commissioning run of SeaQuest. Four additional v1495 modules were added to facilitate thorough pulser testing of the firmware designs and in-situ pulser tests of all compiled firmware. These pulser tests proved crucial for diagnosing many errors that may have otherwise gone unnoticed. A significant change to the internal clocking of the trigger system eliminated a subtle source of rate-dependent trigger efficiency. With this upgrade, the trigger finally meets the "dead-time free" design specification.
Drell-Yan dimuon data have been collected and analyzed for central θCS, with nearly flat acceptance in ϕCS, in the mass range 5.0GeV < M_ɣ* < 10.0 GeV at forward x_F with the SeaQuest spectrometer at FNAL. A very preliminary extraction of ƛ has been performed, and the remaining difficulties in extracting ν have been evaluated. Although the results are not yet publishable, significant progress has been made in developing this very challenging angular distributions analysis. A simple scheme for correcting for the angular acceptances of the spectrometer, trigger, and reconstruction has been developed and demonstrated. A generally applicable correction for the kinematically-dependent, rate-dependent reconstruction efficiency has been developed and applied to all current analyses on SeaQuest data. This rate-dependence correction was the first major hurdle in the path to publication of many preliminary SeaQuest results. The last remaining major correction for all analyses, but especially important for the angular parameter extraction, is the full characterization, rate-dependence correction, and subtraction of the combinatoric background contribution to the reconstructed dimuon sample.
Independently, an intuitive, kinematic derivation of the single-event definitions of the Drell-Yan angular parameters has been developed under the assumption of unpolarized annihilating quarks within unpolarized nuclei. At O(α_s), where the quarks remain co-planar with the hadrons in the photon rest frame, this kinematic method reproduces the Lam-Tung relation and derives an additional equality for μ^2, which is only interpretable for single-event parameters. This method has been extended to the case of quark non-coplanarity, and the coplanar equalities become inequalities. A new equality was discovered, which should be obeyed by single-event parameters even in the case of a non-coplanar quark axis. The non-coplanar parameter relations have been used to derive constraints on the experimentally accessible values of ƛ and v. These constraints are compared with existing data and have been found consistent, except in the cases where significant contributions from non-zero Boer-Mulders functions are expected. Finally, the kinematically-derived parameter definitions have been applied to high-precision CMS data. The relative contributions of the q(bar q) and qg processes to the Z-boson "Drell-Yan" cross-section have been extracted. Further, an average measure of non-coplanarity, likely caused by O(α_s^2) and higher processes, has been extracted.
Drell-Yan; Hadron; Proton; Angular; Distributions; SeaQuest; Fermilab; Dilepton; Dimuon; Collisions
Thu, 07 Jul 2016 00:00:00 GMThttp://hdl.handle.net/2142/930352016-07-07T00:00:00ZMcClellan, Randall EvanUniversal properties of low-temperature glass
http://hdl.handle.net/2142/93012
Universal properties of low-temperature glass
Zhou, Di
Amorphous solids (glasses) present universal properties strikingly different from that of crystalline counterparts at low temperatures, regardless of their microscopic nature. Tunneling-two-level-system model (TTLS model) successfully explained several universalities below 1K, but it cannot explain the other glass low-temperature universal properties. Based on virtual phonon exchange interaction, we develop a glass generic coupled block model to discuss two universal properties: sound velocity/dielectric constant shift, and low-temperature mechanical avalanche problem. We also successfully explain the universal property of glass Meissner-Berret ratio by using our generic coupled block model.
Tunneling-two-level-system (TTLS); Universality; Glass
Mon, 20 Jun 2016 00:00:00 GMThttp://hdl.handle.net/2142/930122016-06-20T00:00:00ZZhou, DiAvalanches in plastic deformation: maximum velocity statistics, finite temperature effects, and analysis of low time resolution data
http://hdl.handle.net/2142/93010
Avalanches in plastic deformation: maximum velocity statistics, finite temperature effects, and analysis of low time resolution data
Leblanc, Michael P
In both crystalline and amorphous solids, plastic deformation consists of intermittent jumps called avalanches, whose sizes are power-law-distributed over a scaling regime. In this thesis, we study the statistics of a simple mean-field avalanche model, with emphasis on both theoretical calculations and application to the analysis of experimental data on material deformation.
We establish a relationship between the simple mean-field model and a continuous time model called the ABBM model, originally proposed as a phenomenological model of Barkhausen noise in magnets. The relationship is formally valid for ductile materials without significant weakening, but the results of our calculations are expected to apply to the small avalanches even in materials with high weakening.
We then use the ABBM model to calculate several exact results concerning a system's maximum velocity during an avalanche. We find that the scaling of the maximum velocity distribution agrees with experiments on crystal plasticity. Left over from our calculations are several experimental predictions ready to be tested. The maximum velocity is a robust experimental observable and it has several distinct advantages over the more commonly-considered avalanche durations, so we expect our predictions to be useful in future tests of avalanche statistics in experimental systems.
Then, motivated by recent creep deformation experiments that find scale-invariant avalanches, we develop a scaling theory for thermally-activated avalanches in the simple avalanche model near the critical point and at low temperature. We highlight several generic predictions for how statistical observables scale with temperature.
Finally, we use the simple avalanche model to study how experimental avalanche measurements are influenced by the time resolution of the data. Using both experimental data and simulation data from the model, we determine how measured quantities change with resolution. From these relationships, we develop methods to diagnose when the time resolution low enough that it changes the measured avalanche statistics. We also propose a new analysis method that allows us to extract accurate size statistics from low-resolution data, and show that it is successful both on simulation data and downsampled high-resolution experimental data.
Avalanches; Nonequilibrium Statistical Mechanics; plastic deformation
Thu, 30 Jun 2016 00:00:00 GMThttp://hdl.handle.net/2142/930102016-06-30T00:00:00ZLeblanc, Michael PSoft matter in motion: from actin to active emulsions
http://hdl.handle.net/2142/92905
Soft matter in motion: from actin to active emulsions
Tsang, Chi Hang Boyce
Using microscope as a discovery tool, we surveyed a range of soft material systems, including filamentous actin, liquid crystal droplet and block copolymer to study their dynamics under equilibrium and non-equilibrium conditions. By following the motion of filamentous actin under a fluorescence microscope, we directly observed a width-varying confinement tube in an entangled solution and its implication on the dynamics of polymers. We then considered the correlation between motions of different filamentous actin to study how the unique structure actin network led to such correlation. On the other hand, liquid crystal droplets under concentrated surfactant solution were observed to slowly solubilize into an aqueous phase. During this time, the oscillatory aggregation was tracked and we studied the mechanism of this self-oscillation. On a smaller scale, communication could be observed among individual droplets using polarized light microscopy. Lastly, we studied the photosensitivity of an azobenzene-funcationalized triblock copolymer with a customized microscope with blue and ultraviolet light illumination.
Soft material; microscopy; image processing
Tue, 28 Jun 2016 00:00:00 GMThttp://hdl.handle.net/2142/929052016-06-28T00:00:00ZTsang, Chi Hang BoyceIn search of photonic bound entanglement: using hyperentanglement to study mixed entangled states
http://hdl.handle.net/2142/92823
In search of photonic bound entanglement: using hyperentanglement to study mixed entangled states
Sharma, Aditya Nilakantan
Quantum entanglement exhibits various interesting features that emerge only in high-dimensional systems. One of the most fascinating is bound entanglement, entanglement that cannot be extracted using local operations and classical communication. This thesis describes our work towards an experimental realization of the four-qubit bound-entangled Smolin state, using the polarization and spatial mode of photon pairs. We describe a number of interesting experimental challenges that this work faced. We present our results on entangled two-qubit spatial mode states and hyperentangled four-qubit polarization-spatial-mode states generated by spontaneous parametric down-conversion from a second-order TEM mode pump. Some of the subtleties involved in preparing genuine mixed states in the lab are discussed.
Entanglement; Hyperentanglement; Bound entanglement; Smolin state; Spontaneous parametric downconversion
Wed, 13 Jul 2016 00:00:00 GMThttp://hdl.handle.net/2142/928232016-07-13T00:00:00ZSharma, Aditya NilakantanFirst principles quantum Monte Carlo study of correlated electronic systems
http://hdl.handle.net/2142/92794
First principles quantum Monte Carlo study of correlated electronic systems
Zheng, Huihuo
The many-body correlation between electrons is the origin of many fascinating phenomena in condensed matter systems, such as high temperature superconductivity, superfluidity, fractional quantum Hall effect, and Mott insulator. Strongly correlated systems have been an important subject of condensed matter physics for several decades, especially after the discovery of high temperature cuprate superconductors. In this thesis, we apply first principles quantum Monte Carlo (QMC) method to several representative systems to study the electron correlations in transition metal oxides (vanadium dioxide) and low dimensional electronic systems (graphene and graphene-like two dimensional systems).
Vanadium dioxide (VO2) is a paradigmatic example of a strongly correlated system that undergoes a metal-insulator transition at a structural phase transition. To date, this transition has necessitated significant post-hoc adjustments to theory in order to be described properly. We apply first principles quantum Monte Carlo (QMC) to study the structural dependence of the properties of VO2. Using this technique, we simulate the interactions between electrons explicitly, which allows for the metal-insulator transition to naturally emerge, importantly without ad-hoc adjustments. The QMC calculations show that the structural transition directly causes the metal-insulator transition and a change in the coupling of vanadium spins. This change in the spin coupling results in a prediction of a momentum-independent magnetic excitation in the insulating state. While two-body correlations are important to set the stage for this transition, they do not change significantly when VO2 becomes an insulator. These results show that it is now possible to account for electron correlations in a quantitatively accurate way that is also specific to materials.
Electron correlation in graphene is unique because of the interplay of the Dirac cone dispersion of pi electrons with long range Coulomb interaction. The random phase approximation predicts no metallic screening at long distances and low energies because of the zero density of states at Fermi level. It is thus interesting to see how screening takes place in graphene at different length scales. We addressed this problem by computing the structure factor S(q) and S(q, ω) of freestanding graphene using ab initio fixed-node diffusion Monte Carlo and the random phase approximation. The X-ray measured structure factor is reproduced very accurately using both techniques, provided that sigma-bonding electrons are included in the simulations. Strong dielectric screening from sigma electrons are observed, which redshifts the pi plasmons resonance frequency at long distance and reduces the effective interactions between pi electrons at short distance. The short distance screening makes suspended graphene a weakly correlated semimetal which otherwise would be an insulator.
The third piece of works is dedicated to studying the low energy excitation of many-body systems using extended Koopmans' theorem (EKT). The EKT provides a straight forward way to compute charge excitation spectra, such as ionization potentials, electron affinities from any level of theory. We implemented the EKT within the QMC framework, and performed systematic benchmark studies of ionization potentials of the second- and third-row atoms, and closed- and open-shell molecules. We also applied it to compute the quasiparticle band structure of solids (graphene).
For complex correlated systems, identifying relevant low energy physics degrees of freedom is extremely important to understanding the system's collective behavior at different length scales. In this sense, bridging the realistic systems to lower energy effective lattice models that involve fewer but important degrees of freedom is significant to understanding correlated systems. We have formulated three ab initio density matrix based downfolding (AIDMD) methods to downfold the ab initio systems into effective lattice models. We have demonstrated the successfulness of these methods by applying them to molecules (H2) and periodic systems (hydrogen chain and graphene).
Quantum Monte Carlo; electronic structure; strongly correlated system; vanadium dioxide; graphene; effective model; extended Koopmans' theorem
Tue, 12 Jul 2016 00:00:00 GMThttp://hdl.handle.net/2142/927942016-07-12T00:00:00ZZheng, HuihuoNuclear dependence of proton-induced Drell-Yan dimuon production at 120 GeV at SeaQuest
http://hdl.handle.net/2142/92782
Nuclear dependence of proton-induced Drell-Yan dimuon production at 120 GeV at SeaQuest
Dannowitz, Bryan Paul
A measurement of the atomic mass (A) dependence of Drell-Yan (p + A → μ+μ− + X) dimuons produced by 120 GeV protons is presented here. The data was taken by the SeaQuest experiment at Fermilab using a proton beam extracted from its Main Injector. Over 61,000 dimuon pairs were recorded with invariant mass between 4.2 and 10GeV and target parton momentum fraction x2 between 0.1 and 0.5 for nuclear targets H, d (deuterium), C, Fe, and W. The ratio of Drell-Yan dimuon yields per nucleon (Y) for heavy nuclei over deuterium, R = Y(A)/Y(d), is approximately equal to the ratio of the distributions of anti-up quarks in the two nuclei. This measurement is therefore sensitive to modifications in the anti-quark sea distributions in nuclei for the case of proton-induced Drell-Yan. The data analyzed here and in the future of SeaQuest will provide tighter constraints on various models that attempt to define the anomalous behavior of nuclear modification as seen in deep inelastic lepton scattering, a phenomenon generally known as the EMC effect.
Nuclear Physics; Drell-Yan; Experimental Physics; Electromagnetic compatibility (EMC) effect;
Tue, 12 Jul 2016 00:00:00 GMThttp://hdl.handle.net/2142/927822016-07-12T00:00:00ZDannowitz, Bryan PaulPrecise measurement of mixing parameters and sterile neutrino search at Daya Bay
http://hdl.handle.net/2142/92705
Precise measurement of mixing parameters and sterile neutrino search at Daya Bay
Huang, En-Chuan
Neutrino oscillation with three active neutrinos has been well established by experiments. However, θ_13 was the least known mixing angle before the Daya Bay reactor neutrino experiment. The Daya Bay experiment uses relative measurement with eight identically-designed antineutrino detectors (ADs) located in two near sites, each with two ADs, and one far site with four ADs. In 2012, Daya Bay first observed the non-zero value of (sin^2)2θ_13 at a > 5σ significance with the initial six ADs. In the summer of 2012, the last two ADs were installed to complete the full configuration. In this thesis, the data set of 217 days of 6-AD data and 404 days of 8-AD data were analyzed. The reactor electron antineutrinos ν_e were observed via the inverse beta decay reaction, v_e + p → (e^+) + n. The v_e events were selected by the delayed coincidence between the (e^+) signal and the neutron capture occurring on average 30 μs later. The data quality was carefully checked. A (Χ^2) analysis was constructed with nuisance parameters to consider the detector-related and the background uncertainties and a covariance matrix to encapsulate the reactor uncertainties. This analysis found (sin^2)θ2_13 =0.083 ± 0.0047 and Δ[(m^2)_32] = (2.43 ± 0.10) x (10^-3) e(V^2), assuming normal mass hierarchy. Furthermore, a search for the sterile neutrinos, neutrinos that do not interact weakly with matter, was conducted. A combined analysis with the Bugey and MINOS experiments was performed, and the result was directly compared with the allowed regions set by the LSND and MiniBooNE experiments.
Daya Bay; neutrino oscillation; theta13
Wed, 25 May 2016 00:00:00 GMThttp://hdl.handle.net/2142/927052016-05-25T00:00:00ZHuang, En-ChuanTopics in quantum field theory and holography
http://hdl.handle.net/2142/92702
Topics in quantum field theory and holography
Parrikar, Onkar
In the first part of this thesis, we will study free fermions as models for topological insulators, on gravitational backgrounds which include both torsion and curvature, in d = 2 + 1 and d = 4 + 1 dimensions. We compute the parity-odd effective actions for these systems, and use these effective actions to deduce the structure of anomalies (in particular, the torsional contributions) in the edge states which live on the boundary between two different bulk phases. We also give intrinsic, microscopic derivations of these torsional anomalies by considering Hamiltonian spectral flow for edge states in the presence of torsion. All of these calculations fit perfectly within the well-known framework of anomaly inflow, and extend the framework to include torsional contributions. Furthermore, our condensed-matter-inspired setup provides natural resolutions to some previously ill-understood ultraviolet divergences in intrinsic edge calculations of torsional anomalies.
In the second part of this thesis, we consider the Bosonic and Fermionic U(N) vector models close to their free fixed points, with single-trace deformations turned on. We derive the higher-spin holographic duals corresponding to these vector models by first formulating these theories in terms of the geometry of infinite jet bundles, and then interpreting the renormalization group equations for single-trace deformations as Hamilton's equations of motion on a one-higher dimensional emergent spacetime. We evaluate the resulting bulk on-shell action explicitly, and show that it reproduces all the correlation functions of the vector models. Furthermore, we show that the linearized bulk equations of motion contain the Fronsdal equations of motion on Anti-de Sitter space, thus proving equivalence with Vasiliev higher-spin theories to linearized order. The bulk theory we derive is consistent with the known AdS/CFT framework, and gives a concrete boundary to bulk implementation of AdS/CFT as a geometrization of the renormalization group.
Quantum Field Theory; Holography
Fri, 03 Jun 2016 00:00:00 GMThttp://hdl.handle.net/2142/927022016-06-03T00:00:00ZParrikar, OnkarStochastic dynamics in spatially extended physical and biological systems
http://hdl.handle.net/2142/92701
Stochastic dynamics in spatially extended physical and biological systems
Jafarpour, Farshid
In this thesis, I discuss three different problems of stochastic nature in spatially extended systems: (1) a noise induced mechanism for the emergence of biological homochirality in early life self-replicators, (2) the amplification effect of nonnormality on stochastic Turing patterns in reaction diffusion systems, and (3) the velocity statistics of edge dislocations in plastic deformation of crystalline material.
In Part I, I present a new model for the origin of homochirality, the observed single-handedness of biological amino acids and sugars, in prebiotic self-replicator. Homochirality has long been attributed to autocatalysis, a frequently assumed precursor for self-replication. However, the stability of homochiral states in deterministic autocatalytic systems relies on cross inhibition of the two chiral states, an unlikely scenario for early life self-replicators. Here, I present a theory for a stochastic individual-level model of autocatalysis due to early life self-replicators. Without chiral inhibition, the racemic state is the global attractor of the deterministic dynamics, but intrinsic multiplicative noise stabilizes the homochiral states, in both well-mixed and spatially-extended systems. I conclude that autocatalysis is a viable mechanism for homochirality, without imposing additional nonlinearities such as chiral inhibition.
In Part II, I study the amplification effect of nonnormality on the steady state amplitude of fluctuation-induced Turing patterns. The phenomenon occurs generally in Turing-like pattern forming systems such as reaction-diffusion systems, does not require a large separation of diffusion constant, and yields pattern whose amplitude can be orders of magnitude larger than the fluctuations that cause the patterns. The analytical treatment shows that patterns are amplified due to an interplay between noise, non-orthogonality of eigenvectors of the linear stability matrix, and a separation of time scales, all built-in feature of stochastic pattern forming systems. I conclude that many examples of biological pattern formations are nonnormal stochastic patterns.
In Part III, I study the dynamics of edge dislocations with parallel Burgers vectors, moving in the same slip plane, by mapping the problem onto Dyson's model of a two-dimensional Coulomb gas confined in one dimension. I show that the tail distribution of the velocity of dislocations is power-law in form, as a consequence of the pair interaction of nearest neighbors in one dimension. In two dimensions, I show the presence of a pairing phase transition in a system of interacting dislocations with parallel Burgers vectors. The scaling exponent of the velocity distribution at effective temperatures well below this pairing transition temperature can be derived from the nearest-neighbor interaction, while near the transition temperature, the distribution deviates from the form predicted by the nearest-neighbor interaction, suggesting the presence of collective effects.
Demographic Noise; Nonequilibrium; Stochastic; Homochirality; Nonnormality; Dislocation Dynamics; Spatial Extension; Turing Patterns; Stochastic Patterns
Thu, 19 May 2016 00:00:00 GMThttp://hdl.handle.net/2142/927012016-05-19T00:00:00ZJafarpour, Farshid